The present invention relates to a technique for manufacturing a resin-sealed type semiconductor device using a lead frame and more particularly to a technique effective in its application to the manufacture of a semiconductor device (a non-leaded type semiconductor device) in which external electrode terminals are exposed to mounting side faces without intentional projection sideways of a package, such as SON (Small Outline Non-Leaded Package) and QFN (Quad Flat Non-Leaded Package).
In the manufacture of a resin-sealed type semiconductor device there is used a lead frame. The lead frame is fabricated by forming a metallic plate into a desired pattern by blanking with a precision press or by etching. The lead frame has a tab for fixing a semiconductor element (semiconductor chip), a support portion called die pad, and plural leads whose front ends (inner ends) face an outer periphery of the support portion. The tab is supported by tab suspension leads extending from a frame portion of the lead frame.
In manufacturing a resin-sealed semiconductor device with use of such a lead frame, a semiconductor chip is fixed to the tab of the lead frame, electrodes on the semiconductor chip and the front ends, or the inner ends, of the leads are connected together using conductive wires, then the inner end sides of the leads, including the wires and the semiconductor chip, are sealed with an insulating resin to form a seal member (package), thereafter, an unnecessary lead frame portion is cut off and at the same time lead portions and tab suspension lead portions projecting from the package are cut off.
On the other hand, as one of resin-sealed type semiconductor devices manufactured using a lead frame there is known a semiconductor device (non-leaded type semiconductor device) wherein a package is formed by one-side molding on one side of a lead frame and leads as external electrode terminals are exposed to one side of the package, without intentional projection of the leads from a peripheral surface of the package. As this type of semiconductor devices there are known an SON wherein leads are exposed to both side edges of one surface of a package and a QFN wherein leads are exposed to four sides of one surface of a quadrangular package.
As an example of a bleeding preventing technique there is known a technique disclosed in Japanese Published Unexamined Patent Application No. Hei 11(1999)-345897. In this unexamined publication is disclosed Fan-out-BGA of a structure having been subjected to processing for the prevention of bleeding of Ag paste, such as the formation of a solder resist dam or blasting (abrasive polishing).
On the other hand, in Japanese Published Unexamined Patent Application No. 2000-196006 is disclosed a QFP (Quad Flat Package) type semiconductor device of a structure wherein lugs projecting toward the interior of a sealing resin are formed on side faces of a die pad for the purpose of improving a close adherence between the die pad and the sealing resin and also improving moisture resistance. According to the structure of this semiconductor device, the back side of the die pad is exposed from the sealing resin.
Further, in Japanese Published Unexamined Patent Application No. Hei 11(1999)-251494 is disclosed a high-frequency device having a gull wing type wire structure for use in a portable telephone or the like in which a semiconductor element mounting portion serves as ground. According to the technique disclosed therein, not only electrodes on a semiconductor element and the leads are connected together through wires, but also the electrodes on the semiconductor element and the semiconductor element mounting portion are connected together through wires because of a die pad serving as ground. This is called down bonding in the literature just referred to above. Because of down bonding, the semiconductor element mounting portion is larger than the semiconductor element, and in a mounted state of the semiconductor device the semiconductor element mounting portion projects to the outside of the semiconductor device.
From the standpoint of reducing the size of a semiconductor device and preventing bending of leads serving as external electrode terminals there is used a non-leaded type semiconductor device using one-side molding such as SON or QFN. In a non-leaded type semiconductor device, lead surfaces exposed to one surface of a package constitute a mounting surface and therefore the mounting area is small in comparison with SOP (Small Outline Package) and QFP in which leads are projected from side faces of a package.
In a non-leaded type semiconductor device of a tab exposed structure there exists a keen demand for a down bonding structure wherein electrodes on a semiconductor element (semiconductor chip) and a tab with the chip mounted thereon are connected together using wires, with a view to improving electrical characteristics of particularly a high-frequency device. Thus, it is now a pressing need to develop a package structure which permits down bonding while ensuring high reliability.
In a non-leaded type semiconductor device wherein a tab is larger than a chip, a surface (main surface) of the tab with the chip mounted thereon and resin which constitutes a packages are apt to be peeled off from each other. This peeling-off is ascribable to a one-side molded structure wherein the surface (main surface) of the tab is in contact with the resin, while the back side of the tab is exposed from the resin, and is also ascribable to a thermal stress (thermal strain) induced by a difference in thermal expansion coefficient, xcex1, among components.
As an example, the semiconductor element is formed of silicon (xcex1=3.0xc3x9710xe2x88x926/xc2x0 C.), while the tab and leads are formed of Cu (xcex1=1.7xc3x9710xe2x88x925/xc2x0 C.). An adhesive for connection between the semiconductor element and the tab is Ag paste (xcex1=3.5xc3x9710xe2x88x925/xc2x0 C.) constituted by an epoxy resin, wires connected to electrodes on the semiconductor element are Au wires (xcex1=2.63xc3x9710xe2x88x925/xc2x0 C.), and the resin which constitutes a package is a biphenyl resin (xcex1=1.2xc3x9710xe2x88x925/xc2x0 C.).
In the case of a mounting substrate with a non-leaded type semiconductor device mounted thereon, such as a mother board, e.g., FR-4, the value of xcex1 is 1.5xc3x9710xe2x88x925/xc2x0 C.
Thus, due to a difference in thermal expansion coefficient among components which constitute a non-leaded type semiconductor device or due to a difference in thermal expansion coefficient of the mounting substrate before and after mounting, a strong internal stress is imposed on the tab surface-resin interface, thus making peeling-off of the tab from the resin (package) easier.
To permit down bonding, Ag plating is needed for connecting wires (Au wires) to the tab surface, but the presence of this plating film further deteriorates a close adherence between the tab surface and the resin, thus making peeling-off easier between the tab surface and the resin.
For mounting (fixing) the chip there is used an adhesive such as Ag paste, but in the case of a structure wherein Au wires are connected directly to the tab surface, a liquid component contained in the adhesive bleeds (bleeding phenomenon) and forms a film on the Ag plating, which impedes the bonding (connection) of Au wires, causing lowering of bonding strength and consequent separation. Such lowering of the wire bonding strength caused by the bleeding phenomenon is not limited to the case of Au wire and Ag plating but occurs also in the case of other wires and other plating films.
A gap is formed as a result of peeling-off between the tab surface and the resin. This gap acts as a path of water incoming from the exterior of the package, thus deteriorating the reliability of the down-bonded portion. Particularly, in a tab-exposed type package, it is difficult to ensure a sufficient strength of contact with resin because neither side of the tab is sealed with resin. Moreover, since the tab is not covered with resin, the temperature of the tab becomes very high under heating by a heater during mounting such as solder reflow and therefore the water staying in the gap formed by peeling-off between the tab surface and the resin expands. Consequently, the fear of breakage of the package increases. Such a problem becomes more conspicuous in the case of connecting the back side of the tab with electrodes on a wiring board through solder.
It is an object of the present invention to provide a semiconductor device and a non-leaded type semiconductor device which are high in the reliability of wire connection.
It is another object of the present invention to provide a semiconductor device and a non-leaded type semiconductor device which are high in the reliability of connection of the down-bonded portion.
It is a further object of the present invention to provide a semiconductor device and a non-leaded type semiconductor device which are capable of preventing peeling-off between a tab surface and a package-constituting resin.
It is a further object of the present invention to provide a semiconductor device and a non-leaded type semiconductor device which are high in a close adherence between a semiconductor device mounting tab and a package constituting resin and also high in moisture resistance.
The above and other objects and novel features of the present invention will become apparent from the following description and the accompanying drawings.
The following is a brief description of typical inventions out of those disclosed herein.
(1) A semiconductor device comprising:
a seal member formed of an insulating resin;
a tab whose back side is exposed to a mounting surface of the seal member, the tab having, on a surface thereof opposite to the back side, a semiconductor element fixing area and wire connection areas;
tab suspension leads exposed to the mounting surface of the seal member and contiguous to the tab;
a plurality of leads whose back sides are exposed to the mounting surface of the seal member;
a semiconductor element positioned within the seal member and fixed through an adhesive onto the semiconductor element fixing area on the surface of the tab in such a manner that a back side thereof is opposed to the tab surface;
a plurality of electrodes formed on a main surface of the semiconductor element;
electrically conductive wires for electrically connecting the plural electrodes and surfaces of the leads with each other; and
electrically conductive wires for electrically connecting the electrodes on the semiconductor element and the wire connection areas on the tab with each other,
characterized in that the tab is formed larger than the semiconductor element so that outer peripheral edges of the tab are positioned outside outer peripheral edges of the semiconductor element, and
a groove is formed in the surface of the tab so as to be positioned between the semiconductor element fixing area and the wire connection areas.
The aforesaid groove surrounds the whole circumference of the semiconductor element fixing area. The adhesive is not applied to the wire connection areas on the tab. A plating film is formed selectively on the wire connection areas of the tab and the surfaces of the leads, and the wires are connected onto the plating film. The area of the surface of the tab is larger than that of the back side of the tab. The tab has a section which is in the shape of an inverted trapezoid. The adhesive is applied also to the interior of the groove and the semiconductor element is larger than the semiconductor element fixing area and is fixed also onto the groove through the adhesive. The groove is selectively formed correspondingly to areas where the wires are connected. The tab is quadrangular. The groove is selectively formed in a mutually independent manner without being formed at four corners of the tab. The groove is selectively formed in a mutually independent manner along sides of the quadrangle of the tab. Grooves are formed in the surfaces of the leads respectively and the wires are connected at positions closer to the semiconductor element with respect to the grooves formed in the surfaces of the leads.
According to the above means (1), (a) since the tab is larger than the semiconductor element so that outer peripheral edges thereof are positioned outside outer peripheral edges of the semiconductor element, the electrodes on the semiconductor element can be connected (down-bonded) to any nearby positions on the tab surface. In this case, since a tab surface portion is present outside the whole circumference of the semiconductor element, the down-bonding wires can be made shortest in length. In down bonding, ground electrodes are connected to the tab surface which serves as a common ground. In this case, any ground electrodes on the semiconductor element can be connected to nearby tab surface portions, so where the semiconductor device is a high-frequency device, it is possible to stabilize the ground potential of circuit.
(b) In a tab surface portion located between the semiconductor element fixing area to which the semiconductor element is fixed and the wire connection areas to which down-bonding wires are connected there is formed a groove so as to surround the semiconductor element fixing area. Therefore, the bleeding phenomenon that the resin component present within the Ag paste oozes out to the tab surface and reaches the wire connection areas is stopped in the groove portion; in other words, the resin component thus oozing out can be prevented from reaching the wire connections beyond the groove. That is, the adhesive is not present outside the groove. As a result, the wires are connected onto the Ag plating film without being connected onto the resin component as in the prior art, thus permitting strong connection of the wires and improving the reliability of wire connection. That is, the reliability of down-bonding connection is improved.
(c) As mentioned in the above (b), since the bleeding of the resin component from Ag paste is stopped in the aforesaid groove, the bleeding area of the resin component becomes smaller than in the prior art and hence it is possible to prevent lowering of the bonding force between the tab and the resin. As a result, the tab-resin peeling off becomes difficult to occur and the moisture resistance of the package is improved.
(d) Since the resin which forms the package enters the foregoing groove, the tab-package bonding area (close contact area) becomes wider than in the prior art and the tab-resin bonding force becomes high, thus resulting in that the tab and the package (resin) become difficult to peel off from each other and the moisture resistance of the package is improved.
(e) Since the foregoing groove is present, in the case where the tab-package peeling-off occurs at a portion where an internal stress at the tab-resin interface is large and the bonding strength is low, such as an Ag paste-applied portion or an Ag-plated portion, it is possible to prevent propagation of the tab-resin peeling-off and hence prevent the formation of a large gap which would induce the entry of water.
According to the structure using the groove portion to prevent bleeding, in comparison with other bleeding preventing methods, not only it is easy to fabricate the groove portion from the metallic plate as the material of the lead frame but also it is not necessary to ensure a margin for a plane layout of both chip mounting portion and groove portion; besides, even part of the groove can be disposed under the chip. Therefore, it is possible to realize the reduction in size of the tab. Especially in the case of a package of the type wherein leads are arranged around a tab, it is possible to realize the reduction in size of the package.
(f) The section of the tab is in the shape of an inverted trapezoid and the area of the tab surface for fixing the semiconductor element is larger than that of the back side of the tab. Therefore, tab ends are of a sectional shape with sharp ends, which bite and are buried into the resin, thus making it difficult for the tab to peel off from the package.
(g) In the structure wherein the tab is in the shape of an inverted trapezoid and a groove is formed in the tab surface, no lug is formed on the tab surface. Thus, by adopting a tab shape with no lug present around the chip mounting area (semiconductor element fixing area), it is possible to make a wire loop small. Particularly, by making the wire loop length small, it is possible to arrange leads in the vicinity of the tab, whereby it is possible to attain the reduction in size of the package. Further, by making the wire loop height small it is possible to decrease the height of the seal member and attain the reduction in thickness of the package.
(h) Since each lead is formed with a groove, the area of contact with the resin becomes larger than in the prior art and hence it becomes difficult for the lead to peel off from the resin. Besides, since the resin enters the groove formed in the resin, this bite-in structure makes it even more difficult for the lead to peel off from the resin. Further, since the groove is present, the path of water entering the interior from the peripheral surface of the package along the surfaces of the leads becomes long and hence it is possible to prevent water-corrosion of the wires which are connected to the leads.
(i) Since Ag plating film is formed on the wire connection areas of the leads and the wires are fixed onto the Ag plating film, it is possible to improve the wire connection strength.
(j) According to the structure of the present invention thus permitting the prevention of peeling-off of wire connections and peeling-off between the tab and the resin, it is possible to make an improvement of yield in the manufacture of the semiconductor device and hence possible to reduce the manufacturing cost of the semiconductor device.